Stomach-Churning Germ Infects Alaskan Oysters

WEDNESDAY, Oct. 5, 2005 (HealthDay News) -- Midsummer's sails through Alaska's Prince William Sound last year resulted in nasty diarrheal illness for several dozen passengers who ate raw oysters while on board.

Of even greater significance, however, is the fact that the oysters were infected with an organism, Vibrio parahaemolyticus, that is normally found in waters at least 1,000 kilometers south, indicating that climactic changes may be behind the outbreak, new research suggests.

"Rising temperatures of ocean waters seem to have contributed to one of the largest known outbreaks of V. parahaemolyticus in the United States," said Dr. Joseph McLaughlin, a medical epidemiologist with the Alaska Department of Health and Social Services in Anchorage.

McLaughlin, lead author of the article documenting the findings in the Oct. 6 issue of the New England Journal of Medicine, stopped short of attributing the events to global warming. "We can't speak to why the ocean temperatures rose," he said.

Dr. Paul R. Epstein, associate director of the Center for Health and the Global Environment at Harvard Medical School, added: "It's a very interesting study, one of the first that's really documented such a dramatic shift in latitude into Alaska of a tropical health problem. This is a relative of cholera, and that's not thought to be circulating in Alaska."

Epstein authored an article on global warming that appears in the same issue of the journal and has previously presented papers on V. parahaemolyticus. Not only is he a medical expert on the organism, he is a personal expert, having contracted the illness while eating crabs in eastern Africa.

"It's wicked," he said. "I'm well aware of the illness."

V. parahaemolyticus is the leading cause of gastroenteritis associated with seafood in the United States. It usually results from eating raw or improperly cooked oysters taken from warm-water estuaries.

Between 1995 and 2003, the Alaska Department of Environmental Conservation tested about 400 oysters and other marine samples for the organism and found none; the waters were believed to be too frigid to sustain it.

On July 16, 2004, however, the Alaska health department was notified of an outbreak of gastroenteritis among passengers on a cruise ship sailing Prince William Sound. Three days later, a Nevada health official contacted his Alaska counterparts with news of a diagnosis of laboratory-confirmed V. parahaemolyticus in a Nevada resident. That man had become ill on July 4 while a passenger on the ship, the day after he feasted on raw oysters.

McLaughlin and his colleagues eventually identified 62 patients with gastroenteritis traceable to eating raw oysters, all of them harvested from Alaskan waters with a mean daily temperature of more than 15 degrees Celsius. In all, 29 percent of the people who had eaten the oysters fell ill.

Since 1997, the researchers reported, mean water temperatures during July and August at one of the Alaska oyster farms increased 0.21 degrees Celsius each year. The year 2004 was the only one when the temperatures did not drop below 15 degrees Celsius, the temperature thought to be the cut-off point for supporting dangerous levels of V. parahaemolyticus.

The events of last summer pose new challenges for health officials who are more used to handling Arctic hazards.

"Health officials really need to be aware of the possibility of the emergence of V. parahaemolyticus and, as water temperatures start to approach this 15 degree threshold, they should start to consider control measures for preventing infection," McLaughlin said.

The Alaska outbreak may only signify the tip of the iceberg of global change.

"There are a lot more biological problems related to climate change than is usually considered," Epstein said. "On the one hand, it's not a pretty picture and it's upsetting. On the other hand, it increases the urgency for solutions."

Epstein's article documented increases in illness worldwide as climactic changes have taken place. These include malaria, dengue fever and cholera after Hurricane Mitch inundated Central America in 1998, a fivefold increase in malaria in Mozambique after rain and cyclones in 2000, as well as heat waves across Europe and the United States, along with unprecedented high temperatures.

"As of 2001, we know that climate is changing, that human activities are contributing, that biological systems are reacting to the warming on all continents and that weather is becoming more extreme as oceans heat up," Epstein said. "Biological systems are responding. What we are now seeing in this [Alaskan oyster] example is a dramatic example of where warming to the northern latitudes can allow the northern movement of organisms."

More information

The U.S. Environmental Protection Agency has more on global warming.